Color, diffusion transfer processes of the prior art such as U.S. Pat. No. 2,983,606 generally involve the use of a photographic element comprising a support, at least one silver halide emulsion layer, and contained therein or contiguous thereto a dye developer. A liquid processing composition is applied to the photosensitive element and permeates the emulsion to provide a solution of the dye developer substantially uniformly distributed therein. As the exposed silver halide emulsion is developed, the oxidation product of the dye developer is immobilized or precipitated in situ with the developed silver, thereby providing an imagewise distribution of unoxidized dye developer dissolved in the liquid processing composition. This immobilization is apparently due, at least in part, to a change in the solubility characteristics of the dye developer upon oxidation, and particularly as regards its solubility in alkaline solutions. At least part of this imagewise distribution of unoxidized dye-developer is transferred to a superposed image-receiving layer to provide the transfer image.
The prior art has typically employed positive-working emulsions such as internal image silver halide emulsions and solarizing direct positive silver halide emulsions to produce direct positive color images in a diffusion transfer system. For example, Belgian Pat. No. 788,268 and U.S. Pat. No. 3,725,062 relate to such positive-working emulsions. The use of positive-working emulsions, however, does not offer the high exposure speed obtained with negative emulsions. Typically, positive-working emulsions are relatively difficult to produce.